Digital cameras which make use of image sensors such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor to convert an optical image into an electrical signal, and to record by digitizing the electrical signal, have become very popular in recent years. In this kind of digital camera, there is a need not only for increasing the number of pixels of the CCD or CMOS sensor, but also for improving the performance of the lens barrel which forms the optical image on these image sensors. More specifically, there is a need for a lens barrel equipped with a higher power zoom lens system.
On the other hand, in the field of the digital camera, there is a need for a smaller size body in order to improve portability. To this end, there is a need for reduced size in an image pickup apparatus equipped with a lens barrel and image sensors, which is believed to contribute greatly to reducing the size of the housing. In these efforts to reduce the size of an image pickup apparatus, what is known as a bending optical system has been proposed, in which the apparatus is reduced in size by bending the zoom lens system at some point along the optical path, without changing the optical length.
For example, Patent Document 1 discloses a bending optical system in which the light path is bent using a reflecting mirror. More specifically, the lens barrel disclosed in Patent Document 1 includes, in order from the side of the object, a first lens group and a second lens group, on the side of the reflecting mirror facing the object, and in order from the side of the reflecting mirror, a third lens group and a fourth lens group, on the side of the reflecting mirror facing the image sensor. The first lens group is fixed. The second lens group and the third lens group are movable in the optical axis direction, and make up the zoom lens system in cooperation with each other. The fourth lens group is used for adjusting the focus.
In addition, Patent Document 2 discloses a bending optical system in which the light path is bent using a prism. More specifically, the lens barrel disclosed in Patent Document 2 includes a lens group on the side of the object with respect to the prism. The lens group is movable in the optical axis direction between the in-use position and the retracted position. Furthermore, the prism is movable so that the space in which the lens group is accommodated is secured when the lens group is located at the retracted position.
Furthermore, in Patent Document 3, the configuration of a lens group used in a bending optical system is disclosed.
Patent Document 1: Japan Patent Laid-Open Publication No. H11-258678
Patent Document 2: Japan Patent Laid-Open Publication No. 2003-169236
Patent Document 3: Japan Patent Laid-Open Publication No. 2004-102089